1. Field of the Invention
The present invention concerns a system for regulating the flow of an ink in a graphic process, including:                a reciprocating positive displacement pump, e.g., a piston or membrane pump, connected to a first container via a first liquid conduit and to a printing module in a graphic printing machine via a second liquid conduit, the pump is configured for pumping an ink from the first container and to the graphic printing unit, and wherein the viscosity of the ink affects operation of the pump;        a sensor connected with the pump and which is configured to measure at least the pump strokes in the pump; and        a controller connected with the sensor and which is configured to analyse the data from the sensor and determine the number of pump strokes over a predetermined time period.        
The present invention also concerns a method for regulating the flow of an ink in a graphic process, including the following steps:                pumping an ink by means of a reciprocating positive displacement pump, e.g., a piston or membrane pump, from a container and to a printing module (1a) in a graphic printing unit, and wherein the viscosity of the ink affects operation of the pump;        measuring at least the pump strokes in the pump by means of a sensor; and        wherein data from the sensor are analyzed and the number of pump strokes over a predetermined period of time are determined in a controller.        
2. Description of Related Art
Professional graphic printing machines today need careful control and composition of the various printing inks which are conducted into the printing module in the printing machine in order to attain correct color intensity, brilliance and rubbing resistance on the finished printed matter or article. Therefore, it is necessary to control various properties of each single ink, including viscosity, color composition (mix of ink colors), pigmenting, bonding capability, temperature, flow, etc. during the printing process.
Various systems and methods for measuring and controlling the flow of printing inks are described in the literature. Similarly, various systems and methods for regulating the properties of the inks are described in the literature.
European Patent Application EP 1 138 487 A2 and corresponding U.S. Pat. No. 6,546,681 disclose a system and a method for measuring and regulating the viscosity of ink in a printing machine where the measuring apparatus for measuring the viscosity includes two rotating parts which are magnetically interconnected by means of magnets provided in both parts, of which one part is disposed in the liquid flow after the pump, and the other part is disposed outside the liquid flow. An electric motor rotates the part disposed outside the liquid flow which in turn rotates the other part by means of the magnetic field generated by the magnets. The electric motor is connected with a control unit regulating the speed of the motor so that the parts are rotated at constant speed. The control unit detects the power consumption used for rotating the parts at the constant speed, and then calculates the viscosity of the ink. At least one flowmeter is disposed either before or after the apparatus in order to ensure constant flow through the measuring apparatus. The viscosity is automatically regulated by means of a dosing apparatus which adds a diluent to the ink determined by the measured viscosity.
This system uses up to several measuring units disposed between the pump and the printing unit provided in the printing machine for measuring the flow and viscosity of the ink and a relatively complex regulating system for controlling the viscosity of the ink. These units increase the complexity of the entire plant, raising the cost of the entire plant considerably. Moreover, the various measuring units in the liquid flow require regular maintenance in order to avoid erratic measurements and clogging that may cause the plant to be shut down which in turn raises the total production costs and costs of maintenance.
U.S. Pat. No. 5,027,661 A1 describes a system and a method for measuring the volume of ink in a printing machine wherein the system includes a microphone or a pressure sensor for measuring the outgoing air pressure or pressure variations in the flow to the pump. The microphone/sensor is used for detecting the pump strokes of the pump and is connected to a microprocessor which calculates the number of pump strokes, the speed of the pump and the volume of each pump stroke for the pump in question. The pump strokes are used to determine if the container from which the pump is pumping is about to run dry. The microprocessor can control several pumps individually in order to achieve correct color composition.
This system has the advantage that it does not require one or more external flowmeters disposed in the liquid flow in order to determine the volume of the ink, a fact which contributes to minimise the total costs of the plant.
However, this system has the drawback that it is only possible to determine the volume of the ink from the pump strokes. Since the viscosity influences how much ink is pumped out for each pump stroke, it is necessary manually to determine the viscosity by means of known measuring techniques and to dilute the ink manually. If the viscosity changes, it is necessary to regulate the speed of the pump (number of pump strokes) in order to maintain a constant flow of ink to the printing machine.
U.S. Pat. No. 2,590,538 discloses a rotogravure printing system having a pump configured to pump the ink from a first reservoir to a second reservoir in the printing device. The pump is arranged between a mixing chamber and a manual adjustable valve. The mixing chamber has two inlets connected to the first reservoir and a third reservoir holding a diluent respectively. A pressure sensor connected to a T-junction is arranged between the pump and the adjustable valve. An electrically controlled valve is activated when the pressure in the ink conduit reaches a threshold value, whereby diluent is led into the mixing chamber. As the pressure in the ink conduit drops below the threshold value, the valve is deactivated and the supply of diluent is stopped.